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Lesson 5.4 Community Stability A 2010 report on invasive species suggests that they cost the U.S. $120 billion a year in environmental losses and damages. Catalyst: Vocabulary and Reading Strategy Section in Study Guide Invasive kudzu Lesson 5.4 Community Stability Ecological Disturbances • A community in equilibrium is generally stable and balanced, with most populations at or around carrying capacity. • Disturbances or changes in the environment can throw a community into disequilibrium. • Severe disturbances can cause permanent changes to a community and initiate a predictable series of changes called succession. Forest fire Lesson 5.4 Community Stability Primary Succession • Occurs when there are no traces of the original community remaining, including vegetation and soil • Primary succession begins with bare rock • Pioneer species, such as lichens, are the first to colonize. • The environment changes as new species move in, adding nutrients and generating habitat. Lesson 5.4 Community Stability Primary Succession • Over the course of ecological succession, species diversity increases over time. • Lichens are great pioneer species because they can grow on bare rock. • They are made up of algae that provide food and energy through photosynthesis and fungi that attach to rock and capture moisture. Lesson 5.4 Community Stability Secondary Succession • • • Occurs when a disturbance dramatically alters a community but does not completely destroy it Common after disturbances such as fire, logging, or farming Occurs significantly faster than primary succession Lesson 5.4 Community Stability Primary vs. Secondary Succession Talk about it: What’s the difference between primary and secondary succession? • • Both establish new ecological communities Primary succession begins with no vegetation or soil left behind after the disturbance (ex: volcanic eruption) • • Pioneer species must begin to grow on bare rock Secondary succession begins with vegetation that existed prior to the disturbance Lesson 5.4 Community Stability Succession in Water • Primary aquatic succession occurs when an area fills with water for the first time. • Disturbances such as floods or excess nutrient runoff can lead to secondary aquatic succession. Lesson 5.4 Community Stability Secondary Succession in Water • Occurs when a lake fills in, creating a grassy meadow. 1. Algae and other organisms grow, reproduce, and die, creating nutrients to support more plant life. 2. This gradually fills the pond with organic matter. The lake becomes shallow and marshy as decaying matter piles up. 3. Eventually, the pond may completely fill up and a terrestrial ecosystem can establish itself. Lesson 5.4 Community Stability Climax Communities • Ecologists once thought succession leads to stable “climax” communities. • Today, ecologists see communities as temporary, ever-changing associations of species. • Communities are influenced by many factors and constant disturbances. Beech-maple forest, a classic “climax community” Lesson 5.4 Community Stability Invasive Species • Nonnative organisms that spread widely in a community • A species becomes invasive when a lack of limiting factors such as predators, parasites, or competitors enables their population to grow unchecked. • Not all invasive species are harmful. Did You Know? Although the European honeybee is invasive to North America, it is beneficial because it pollinates our agricultural crops. Cane Toads: An Unnatural History